Hassan Diab as he arrives at the courthouse in Paris in 2016. BERTRAND GUAYBERTRAND / AFP

For the eighth time, a French appeals court has overturned a judicial order to release on bail former Ottawa university professor Hassan Diab.

Since his extradition from Canada three years ago, four judges have ruled that the 63-year-old Canadian citizen should be released from the maximum-security Paris prison where he has been held on pre-trial detention.

Following a now familiar pattern, an appeals court quashed the latest release order Tuesday.

Lebanon-born Diab is the sole suspect in the October 1980 terrorist bombing of a Paris synagogue in which four passers-by were killed and more than 40 injured.

He denies being involved and says he was studying in Beirut at the time of the bombing.

The appeal judges are expected to release the reasons for Tuesday’s decision later this week but they have previously accepted the prosecution’s claim that Diab is a threat to public order and a flight risk.

Diab’s French lawyer William Bourdon says the prosecution appeals are “not judicial but political” and motivated by a reluctance not to appear soft on terrorism.

Investigating Judge Jean-Marc Herbaut, one of the judges who has repeatedly ordered Diab’s release, ended his investigation into the case in July after saying previously that there is “consistent evidence” that Diab is telling the truth.

During his almost three-year investigation, Herbaut visited Lebanon to interview – among others – some of Diab’s contemporaries.

But in a surprise twist to the saga, Diab’s Ottawa lawyer Donald Bayne said a “foreign nation” has intervened with Herbaut and given the judge additional documents.

Diab’s legal representatives refused to name the “foreign nation” but said it is neither Canada nor France.

Bayne told this newspaper there is nothing new in the those documents which he said contain numerous factual errors.

This newspaper has not seen the documents.

But Judge Herbaut has apparently decided to re-open the case three months after announcing its closure to give the new intervention a fair hearing.

After he closed the case in July, the judge gave prosecutors and defence lawyers 30 days to respond with final “observations,” as is normal practice in the French justice system.

Herbaut said that 10 days after receiving those responses, he would rule whether Diab should be released and sent home to Canada, or go to trial for the alleged terrorist offences.

Diab’s French lawyers responded and urged the judge to finally end the case against the academic.

Prosecutors have still not responded and while that is unusual, there is no legal requirement for them to do so.

Diab’s lawyers expect the judge to finally close the case shortly.

Amnesty International, among other groups, has accused the French government of contravening human rights conventions in its treatment of Diab.

The support group “Justice for Hassan Diab” released an open letter to Prime Minister Justin Trudeau on Tuesday signed by prominent Canadians. They are urging Trudeau to intervene in the case.

“Dr. Diab has been pleading for help from the Canadian government in his Kafkaesque situation as he remains imprisoned despite evidence of his innocence,” said Bayne.

Global Affairs Canada said it is closely monitoring the situation and its Paris-based consular officials have visited Diab in jail several times to check on his condition.